The invention relates to an arrangement for growing permanent microbial forms, in particular filamentary microorganisms, as well as for harvesting such permanent forms formed on the surface of a culture medium, which arrangement comprises trays for the culture medium superposed in a box-type container.
These microorganisms, called filamentous constitute an expanded system of branched filaments (hyphae), for instance, hyphomycetes and actinomycetes. Such microorganisms frequently form permanent forms projecting out of the culture medium, primarily if they grow on the surface of a liquid or solid culture medium.
Microbial permanent forms, usually called spores, most frequently are used as the starting culture for fermentations. Thus, i.a., Aspergillus niger spores are employed for the production of citric acid and spores of the germs Trichoderma are used for the production of cellulase. The use of spores has the advantage that the microorganisms, usually highly efficient production strains, can be stored over long periods of time without loosing their activities.
For use in laboratories and pilot plants, it suffices to produce spores from cultures in larger Petri dishes or trays, in which the microorganism grows on solidified liquid culture by finally forming spores, which are then harvested either in a dried state by sterile brushes, or in a wet state by rinsing with a sterile physiologic saline solution.
However, this relatively simple method has the disadvantage that, for one part, only few spores are obtained on Petri dishes and, for the other part, the humidity of the air within a Petri dish can be controlled to an insufficient extent only.
When culturing on larger trays, on the one hand air-conditioned boxes for temperation and, on the other hand, sterile rooms for harvesting the spores must be available. Besides, the sterile manipulation with such trays mostly is very cumbersome.
The control of the humidity of air is of a particular relevance to the quality and to the yield of spores. For this reason, the following mode of procedure has been chosen so far for the production on an industrial scale;
A, usually displaceable, box is equipped with flat superposed and removable trays. These trays are filled with hot, still liquid, culture medium and the entire box including the trays is sterilized in a large-space sterilizer. Upon cooling and solidification of the culture medium, the box is moved out of the sterilizer and is connected to an air-conditioning plant via sterile filters. Thereupon, incubation with spores is effected via the aerating system, the microorganism is grown under an initially high humidity of the air, and upon the formation of spores, desiccation takes place by means of dry air until the culture medium has become dry and the spores, upon removal of the individual trays, can be harvested in a sterile room. Thus, the prerequisite for an industrial production so far has been the availability of a complex and expensive large-space sterilizer. In addition, sterile rooms had to be available for harvesting. Add to this that the transfer of the trays into the sterile room was quite cumbersome and the harvest of the spores involved considerable periods of time. When growing and harvesting spores of pathogenic microorganisms, the personnel, moreover, was hardly able to be protected from contact with the spores during manipulation.